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Date:   Mon, 24 May 2021 11:37:40 +0100
From:   Mark Rutland <mark.rutland@arm.com>
To:     Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] arm64: mm: don't use CON and BLK mapping if KFENCE is
 enabled
Message-ID: <20210524103740.GD1040@C02TD0UTHF1T.local>
References: <20210524153659.58a707a9@xhacker.debian>
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On Mon, May 24, 2021 at 03:36:59PM +0800, Jisheng Zhang wrote:
> Fix below warning if KFENCE=y but RODATA_FULL=n:
> 
> [    0.000000] ------------[ cut here ]------------
> [    0.000000] WARNING: CPU: 0 PID: 0 at mm/memory.c:2462 apply_to_pmd_range+0xec/0x190
> [    0.000000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.13.0-rc1+ #10
> [    0.000000] Hardware name: linux,dummy-virt (DT)
> [    0.000000] pstate: 600000c5 (nZCv daIF -PAN -UAO -TCO BTYPE=--)
> [    0.000000] pc : apply_to_pmd_range+0xec/0x190
> [    0.000000] lr : __apply_to_page_range+0x94/0x170
> [    0.000000] sp : ffffffc010573e20
> [    0.000000] x29: ffffffc010573e20 x28: ffffff801f400000 x27: ffffff801f401000
> [    0.000000] x26: 0000000000000001 x25: ffffff801f400fff x24: ffffffc010573f28
> [    0.000000] x23: ffffffc01002b710 x22: ffffffc0105fa450 x21: ffffffc010573ee4
> [    0.000000] x20: ffffff801fffb7d0 x19: ffffff801f401000 x18: 00000000fffffffe
> [    0.000000] x17: 000000000000003f x16: 000000000000000a x15: ffffffc01060b940
> [    0.000000] x14: 0000000000000000 x13: 0098968000000000 x12: 0000000098968000
> [    0.000000] x11: 0000000000000000 x10: 0000000098968000 x9 : 0000000000000001
> [    0.000000] x8 : 0000000000000000 x7 : ffffffc010573ee4 x6 : 0000000000000001
> [    0.000000] x5 : ffffffc010573f28 x4 : ffffffc01002b710 x3 : 0000000040000000
> [    0.000000] x2 : ffffff801f5fffff x1 : 0000000000000001 x0 : 007800005f400705
> [    0.000000] Call trace:
> [    0.000000]  apply_to_pmd_range+0xec/0x190
> [    0.000000]  __apply_to_page_range+0x94/0x170
> [    0.000000]  apply_to_page_range+0x10/0x20
> [    0.000000]  __change_memory_common+0x50/0xdc
> [    0.000000]  set_memory_valid+0x30/0x40
> [    0.000000]  kfence_init_pool+0x9c/0x16c
> [    0.000000]  kfence_init+0x20/0x98
> [    0.000000]  start_kernel+0x284/0x3f8
> 
> Fixes: 840b23986344 ("arm64, kfence: enable KFENCE for ARM64")
> Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>

It would be good if the commit message could explain the problem more
thoroughly, e.g.

| When we added KFENCE support for arm64, we intended that it would
| force the entire linear map to be mapped at page granularity, but we
| only enforced this in arch_add_memory() and not in map_mem(), so
| memory mapped at boot time can be mapped at a larger granularity.
|
| When booting a kernel with KFENCE=y and RODATA_FULL=n, this results in
| the following WARNING at boot:
|
| < warning here >

With that:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> ---
>  arch/arm64/mm/mmu.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 6dd9369e3ea0..89b66ef43a0f 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -515,7 +515,8 @@ static void __init map_mem(pgd_t *pgdp)
>  	 */
>  	BUILD_BUG_ON(pgd_index(direct_map_end - 1) == pgd_index(direct_map_end));
>  
> -	if (rodata_full || crash_mem_map || debug_pagealloc_enabled())
> +	if (rodata_full || crash_mem_map || debug_pagealloc_enabled() ||
> +	    IS_ENABLED(CONFIG_KFENCE))
>  		flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
>  
>  	/*
> -- 
> 2.31.0
>